Using knowledge and technology, TU Delft’s Faculty of Aerospace Engineering is committed to making aviation as climate neutral as possible. Its scientists cover many themes, from reducing energy consumption, to developing green fuels, electric aircraft and sustainable ground operations. And they all agree that the only way to create sustainable aviation is by addressing the entire system. More sustainable aviation will not be achieved through technology alone. Policy, airline economics and consumer behaviour also play key roles, stresses Arvind Gangoli Rao. “I believe that people have the right to fly, but this right also comes with obligations,” says the Professor of Sustainable Aircraft Propulsion. Aviation is responsible for approximately 2.5% of the global CO₂ emissions. In order to reduce the environmental impact despite the increasing future demand, the Advisory Council for Aviation Research and Innovation in Europe (ACARE) has come up with an ambitious goal: Climate neutrality for aviation by 2050.
The SmartX sustainable aircraft wing being tested at the Open Jet Facility.
© Davide Monteleone/2021
A scale model of a large passenger aircraft with distributed electric propulsion. TU Delft is one of the partners in this Clean Sky 2 Joint Undertaking project, along with Airbus, NLR, ONERA and CIRA, supported by Orange Aerospace.
© Royal NLR
New types of aircraft and fuels
Reaching this target is feasible, says Professor Gangoli Rao, but only by using new types of aircraft and fuels. In the past, as part of the AHEAD (Advanced Hybrid Engines for Aircraft Development) project, the professor developed a completely novel aircraft and engine design that would reduce CO₂ emissions by 65% and NOx emissions by 80%. As Gangoli Rao explains, AHEAD was one of the few projects to propose using clean cryogenic fuels such as Liquid Hydrogen (LH2) or Liquid Natural Gas (LNG), which are promising alternatives for kerosene to achieve the emission reduction. “Hydrogen is now being embraced as the fuel of the future,” says the professor.
While flying on hydrogen is technically possible, incorporating this new fuel into aviation is far from simple. “Not all places in the world will have the capacity and the infrastructure to store and use hydrogen,” explains Gangoli Rao. Which is precisely why his latest research focuses on the flexible use of hydrogen.
‘Realistically, there is no alternative to flying’
TU Delft and sustainable aviation
The Faculty of Aerospace Engineering works on making aviation more sustainable in four areas, addressing the entire aviation system: renewable energy, sustainable operations, materials & structures, and reducing energy consumption. In this article, we highlight studies from the first three themes. On the fourth theme – energy saving – successful designs include: the Flying V (a lighter aircraft with better aerodynamics that saves about 20% fuel); the energy-efficient SmartX aircraft wing (mimics wing movement of birds); and, the TU Delft Laminar Hump (reduces drag).
At the SAM XL field lab, work on the European STUNNING project went on for four years. In a full-scale aircraft fuselage section, innovations were tested in engineering (ultrasonic welding), production and assembly (robots).
Photo: © Henri Werij
Film: NLR
Airport ground operations
“Airports and airport ground operations are important enablers of sustainable aviation,” say Elise Bavelaar and Alexei Sharpanskykh from the Air Transport & Operations group. Working in close collaboration with airports, such as Rotterdam The Hague Airport and Schiphol, the group’s research looks into a variety of topics related to the daily running of airports, such as improving passenger flows in terminals, flight delay predictions and sustainable and autonomous operations. Approximately 10-15% of total aviation-produced emissions are attributed to airport platforms, and ground operations make up around 30% of total airport emissions. The TU Delft scientists are working on algorithms to improve these operations. “Many airports are aiming for emission free ground operations and accommodating electric and/or hydrogen powered aircraft,” says Bavelaar. The researchers are working on a large EU funded project called GOLIAT (Ground Operations of LIquid hydrogen AircrafT) that aims to demonstrate how high-flow liquid hydrogen (LH2) handling and refuelling technologies can be developed and used safely and reliably for airport operations. “Hydrogen powered aircraft are expected to be on the market in the 2030s, but the developments largely focus on hydrogen production and aircraft technology.
BlueSky software for Air Traffic Management
© OculusFilms
Sustainable taxiing
Airport operations are a bit of a blind spot,” explains Sharpanskykh. “Our expertise lies in modelling operations, and we focus on how to prepare the airport infrastructure for hydrogen powered aircraft and enable refuelling and taxiing and other ground operations.” Another line of research the scientists are exploring is sustainable taxiing. “A lot of fuel is burned on the ground, so it’s important to reduce the use of engines once the airplane is on the ground,” says Sharpanskykh. “We are looking at in-wheel electric motors and electric towing vehicles that could be attached to the airplanes and move the aircraft from the runway to the terminal.”
Flameless combustor for hydrogen combustion research.
© OculusFilms
The full-scale Phoenix is a two person aircraft built by the AeroDelft student team to fly on liquid hydrogen.
© AeroDelft
Combination with hydrogen
In the recently completed APPU (Auxiliary Propulsion & Power Unit) project, done in collaboration with Airbus and the French Safran, the TU Delft professor explored combining different engine types and fuels. “Our design combined using kerosene or biofuel for the main engines and using hydrogen or kerosene to run a secondary engine,” explains Gangoli Rao. “This way we could use hydrogen to power the aircraft but in a flexible way.” Just by partly using hydrogen, CO₂ emissions would be reduced by more than 20% and the local air emissions by 40%. “All this without compromising the number of passengers or the range of the aircraft,” adds the scientist. Even though fully hydrogen powered airplanes would reduce emissions much further, flying on a partly hydrogen driven aircraft might be a more realistic option. “It requires less change to the architecture of the aircraft and therefore comes with lower costs,” explains Gangoli Rao. “Using LH2 reduces the climate impact by approximately 60% and increases the costs by 45%. Using the flexible system reduces the climate impact by roughly 50%, but only increases the costs by 20%.” However, making any sustainable changes to aviation requires more than just technological innovation. “Our fuel consumption efficiency continuously increases every year, but so does the number of passengers,” adds the professor. “I don’t blame people. Realistically, there is no alternative to flying. But the right to fly is sometimes misused. There are eight billion people on this planet, but only 10% of those people can fly. And less than 10% of those 10% are responsible for over half the emissions.”
‘Airport operations are a bit of a blind spot’
Single European sky
“I have no faith that the citizens of the world will fly less, and so we will need to solve this issue in other ways,” says TU Delft aviation expert Joris Melkert. He also points out that the biggest step towards sustainable aviation would be to use renewable fuels. “We need to make aircraft more fuel efficient. The most sustainable fuel is the fuel you don’t need.” Melkert also believes that we also need to improve operations in the air and avoid detours. “We should move towards a single European sky, sharing one single airspace across all of Europe,” he says. “Further, there are improvements to be made in ground operations, as well as to the aircraft design itself.” Unfortunately, “we are not doing enough on any these aspects,” Melkert adds. “We know that there are solutions available and where research needs to be done, but it will require a significant amount of time and money. I consider this to be both a technical and a political issue. I’m optimistic that we can make progress, but I’m pessimistic about the timeline.”
Interested in this topic? Explore courses at TU Delft Learning for Life that support professionals throughout their careers, including a course on sustainable aviation.
Materials with lower environmental impact
TU Delft research into aerospace materials could be divided into two main themes, says Rinze Benedictus, Professor of Structural Integrity & Composites. Firstly, developing materials that are reusable. “We are working on materials that come from and can be returned to nature – bioinspired and biomaterials, such as living materials containing fungi,” says Benedictus. “Although this line of research is very exciting and promising, it remains far from real-life application.” Secondly, the scientists are looking at materials that make the energy transition possible. This includes materials for better batteries that could power aircraft, as well as materials that work well with hydrogen. “We are working on a new type of material that can contain hydrogen better, but it is extremely difficult to make,” says the professor. “This is an aspect that is often forgotten – making materials is highly dependent on production technologies. Materials are only one part of the system and if even just one part changes, the entire system breaks down. To really make an impact and make aviation greener, the whole system needs to work together.” Because of the complexity of the entire aviation system, Professor Benedictus does not foresee the use of novel materials in the near future. “In all honesty, there is hardly anything new that I expect to be used in the short term. It will take decades before anything we develop in academia can be used in aviation. There are many promising lines of research that we are pursuing, but to make a real impact in society we need people to pick up what we do.”